Adverse effects on reproductive capacity can occur at every phase of the reproductive process from prenatal development, puberty, to time when conception is occurring and the pregnancy is developing. This research project includes several aspects of the reproductive process, but mostly focuses on factors affecting the ability to conceive and maintain the pregnancy through its first few weeks. The complex biological processes involved include gamete development and maturation, sperm transport through the female reproductive tract, fertilization, early development of the conceptus, implantation, and maintenance of the developing embryo/trophoblast. We have developed methods to estimate environmental effects on fecundability, defined as the per menstrual cycle probability of conceiving, and we have followed women with daily urinary hormone measurements through their pregnancy attempts and early pregnancies. The biological underpinnings of fertility can also influence general health, and we have considered the health effects of female hormones within the framework of this project. The general aims of the project are 1) to refine methods for studying fertility, 2) to provide basic data documenting normal fertility and early development of the conceptus, 3) to investigate the impact of exposures that perturb normal reproductive processes.